Heat exchange of crude oxygen and expanded high pressure nitrogen



Sept. 12, 1967 E. CIMLER ETAL HEAT EXCHANGE OF CRUDE OXYGEN AND EXPANDED HIGH PRESSURE NITROGEN Filed May 6, 1964 mm mwozixm mowmwmai u R E m 0mm 0 20 5503. Emil? ow vow m mfimmumnm 2m: Q 13 u Bod 5 58mi 523% mm m mm in. 0mm mm mm wPm E 1 mm om mmwfi E29 m: A J L zwoomtz mm W moi; zwwca mm ww I 050: @563. mm 53x0 mo A WW E mm a 8v I. 3 NE E r A E E bfi mm 7/ u L 52; Z 4, NV 3v 8 s Q a $85 kiwi E E 1 INVENTOR RAYMOND HIPPELI EDWARD H. VAN BAUSH United States Patent Ofiiice 3 $40 ,697 Patented Sept. 12, 1967 3,340,697 HEAT EXCHANGE OF CRUDE OXYGEN AND EXPANDED HIGH PRESSURE NITROGEN Emil Cimler, Port Washington, Raymond Hippeli, Brooklyn, and Edward H. Van Baush, Pearl River, N.Y., as-

signors to Hydrocarbon Research, Inc., New York,

N.Y., a corporation of New Jersey Filed May 6, 1964, Ser. No. 365,279 5 Claims. (Cl. 62--13) This invention relates to improvements in the separation of air into its various constituents by liquefaction and fractionation.

The production of liquid and gaseous oxygen by the liquefaction and fractionation of air utilizing reversing exchangers for removal of carbon dioxide and water is known.

The purpose of this process is to render the separation more flexible, and of higher efiiciency.

High oxygen vapor product yield can be obtained with simultaneous low nitrogen vapor product yield in one mode of operation. In a second mode of operation, a higher yield of nitrogen vapor can be obtained with a simultaneous lower yield of vapor oxygen. In a third mode of operation, a yield of liquid oxygen or nitrogen can be obtained, equivalent to 2% of the feed air, with simultaneous higher yield of nitrogen and lower yield of oxygen.

Further objects and advantages of this invention will appear from the following description of a preferred form of embodiment thereof when taken with the at tached drawing illustrative thereof, said drawing being a schematic flow sheet of an air liquefaction plant.

Atmospheric air at is filtered at 12, compressed at 14 to approximately 90 p.s.i.a. in compressor 14, cooled to approximately 90 F. in aftercooler 16, and then introduced to surge drum 18. Air then flows to the reversing exchanger system through reversing valves 20, warm reversing exchanger 22, cold reversing exchanger 24 and through the check valves 26, emerging at a temperature of about 275 F. The air then flows in line 28 to the bottom of a high pressure tower 30. The primary air frac tionation takes place in this tower and an overhead vapor nitrogen is withdrawn at 32, partially preheated in reversing exchanger 24, and expanded in turbo expander 34 emergingat 35 at a temperature of approximately -220 F. This relatively warm nitrogen serves to reboil the towel bottoms in exchanger 36 as hereinafter described, and is itself cooled to approximately 275 F. The nitrogen in line 38 is then brought to ambient temperature by passing through reversing exchangers 24 and 22 from which it discharges at 38a as product.

Liquid bottoms in line 40 from the high pressure tower 30 containing approximately 38% oxygen is partially vaporized in exchanger 36 previously described. This is normally accomplished by lines 40a, open valve 73 and open valve 71. The net rich air draw-off liquid 40b from the tower is then sub-cooled in parallel exchangers 42 and 44, passed through line 46 to the acetylene absorbers 48, letdown in pressure to approximately 18 p.s.i.a. in reducing valve 50, passed through nitrogen reflux exchanger 52, and finally fed to an intermediate point in the low pressure tower 54.

Low purity nitrogen liquid is withdrawn at 58 from the high pressure tower 30, such material containing approximately 2% oxygen, is subcooled in exchanger 52, let-down in pressure at 60 to less than 18 p.s.i.a. and fed to the top of the low pressure tower 54.

Oxygen vapor of high purity is withdrawn at 62 from the lower part of the low pressure tower 54 just above the reboiler 64, is passed through exchanger 44 to provide refrigeration for the small rich air stream, and is then warmed up to ambient temperature by passing through reversing exchangers 24 and 22 and ultimately discharging at 62a.

Waste gas containing approximately 2% oxygen is withdrawn at 66 from the top of the low pressure tower 54 and is passed through exchanger 42 to subcool the major stream 40b of rich air, continues to fiow through section 42a and then flows to the reversing exchanger system through the check valves 26, cold reversing exchanger 24, warm reversing exchanger 22, through the reversing valves 21 and finally to atmosphere in 66a.

Within the reversing exchangers the air and waste gas only reverse in the well known manner in order to reject water and carbon dioxide from the plant.

By operating under the first condition, exchanger 36 serves as a reboiler for the high pressure tower. The discharge of the turbo-expander 34 is approximately 220 F.

At this relatively high temperature, the expander discharge flows to exchanger 36 and transfers heat to liquid bottoms from the high pressure tower 30, with the result that some of the bottoms will be returned to the tower as vapor. This gives the high pressure tower 30 more heat affording more duty in exchanger 64 with the result that optimum vapor oxygen can be withdrawn from the plant.

In this mode of operation, the flow of vapor nitrogen at line 32 from high pressur tower 30, expanding in 34 and emerging from the plant at line 38a is minimum and the oxygen flow at line 62 from the low pressure tower 34, emerging from the plant at line 62a is optimum.

Valves 75, 76, 0nd 77 are used to adjust the expander inlet temperature, and therefore the outlet temperature to any desired temperature, depending on the mode of operation.

For alternate operation, exchanger section 42a is put in service to cool the nitrogen in line 32 passing to the expander 34 inlet. Since the expander discharge in this operation would be cold relative to the rich air at the base of the high pressure tower, exchanger 36 performs as a rich air subcooler rather than a reboiler as described initially.

More specifically, some rich .air in line 40 passes through line 40c, valve 72, exchanger 36, through valve 74 and by line 46a, and joins the rich air stream at absorbers 48.

By operating under the second condition, exchanger 36 serves as a sub-cooler for the bottoms in line 40 from the high pressure tower. In this case, the turbo-expander discharge is approximately 300 F.

In this mode of operation the flow of vapor nitrogen at line 32 from high pressure tower 30, expanding in 34, and emerging from the plant at line 38a is increased, with the oxygen flow at line 62a from the plant reduced by lowering the duty at reboiler 64.

In a third mode of operation the expander temperatures and the sub-cooling operation of exchanger 36 are u the same as in the second mode of operation above, with the one exception that there is a greater flow of vapor nitrogen in line 32 from the high pressure tower 30 which is expanded in 34 and emerges as product in line 38a. The increase in expansion flow provides more refrigeration which is transferred to the low pressure tower 54 and permits withdrawal of liquid oxygen from line 68 or liquid nitrogen from line 69.

We believe the method of transferring refrigeration to the nitrogen reflux stream which fiows from the high pressure tower 30 through line 58 to exchanger 52 is unique in that only one liquid stream, the high pressure tower bottoms, take refrigeration from the cold gases in exchangers 42, 44, and 36 and then by means of a very small exchanger transfers refrigeration to the nitrogen liquid in exchanger 52.

Typical examples of operation in accordance with the three modes of operation are as follows:

Mode 1.-Warm expander Product is all vapor with the oxygen amounting to 20.6 volume percent based on 98 percent recovery of the oxygen in the air, together with 9.0 volume percent of nitrogen based on a recovery of 9 percent of the air. This gives the maximum ratio of oxygen to nitrogen.

Mode 2.--Cld expander Product is all vapor with the oxygen amounting to 17.0 volume percent based on 81 percent recovery of the oxygen in the air, together with 18.0 volume percent of nitrogen. This gives a substantially higher yield of nitrogen.

Made 3.C0ld expander with added throughput Product is partly liquid and may be about 10% of the usual oxygen or nitrogen capacity, i.e., 14 volume percent oxygen vapor and 1.6 volume percent liquid. The nitrogen vapor will be in the order of 35 volume percent and depending on operations, the yield of liquid nitrogen, in lieu of liquid oxygen will be 3.5 volume percent.

While we have shown and described a preferred form of embodiment of our invention, we are aware that modifications may be made thereto and we therefore desire a broad interpretation of our invention within the scope and spirit of the description herein and of the claims appended hereinafter.

We claim:

1. The method of separating air to produce vaporous nitrogen and vaporous oxygen which comprises passing said air under a superatmospheric pressure of at least five atmospheres through a heat exchange zone in heat exchange with cold waste gas to lower the temperature of the air to substantially its dew point, introducing said pressurized low temperature air into a high pressure fractionation zone in the presence of reflux to establish a nitrogen vapor overhead, a condensed liquid nitrogen and a crude oxygen liquid bottoms, expanding a first portion of said nitrogen vapor in a turboexpander with work necessary to supply refrigeration for said heat exchange zone, expanding said crude oxygen liquid bottoms into the low pressure fractionation zone, expanding a second liquid portion of said nitrogen into the low pressure fractionation zone to provide reflux and separate a high purity oxygen vapor from a cold waste gas, withdrawing a portion of said crude oxygen liquid bottoms and passing said portion of crude oxygen liquid bottoms in heat exchange with the effluent of the expansion of the first portion of the nitrogen vapor to heat said portion of liquid bottoms, and returning said heat exchanged portion of liquid bottoms back in admixture with the crude oxygen liquid bottoms in said high pressure fractionation zone.

2. The method of separating air to produce vaporous nitrogen and vaporous oxygen which comprises passing said air under a superatmospheric pressure of at least five atmospheres through a heat exchange zone in heat exchange with cold waste gas to lower the temperature of the air to substantially its dew point, introducing said pressurized low temperature air into a high pressure fractionation zone in the presence of reflux to establish a nitrogen vapor overhead, a condensed liquid nitrogen and a crude oxygen liquid bottoms, particularly warming a first portion of said nitrogen vapor, expanding said warm first portion of said nitrogen vapor to supply refrigeration for said heat exchange zone, expanding said crude oxygen liquid bottoms into the low pressure fractionation zone, expanding a second liquid portion of said nitrogen into the low pressure fractionation zone to provide reflux and separate a high purity oxygen vapor from a cold waste gas, and heat exchanging a portion of the crude oxygen bottoms liquid with the efliuent of the expansion of the first portion of the nitrogen, said expanded nitrogen effluent being at a temperature to supply heat to the portion of crude oxygen liquid bottoms and returning said heat exchanged portion of crude oxygen bottoms liquid to said high pressure fractionation zone in admixture with the crude liquid oxygen bottoms to thereby produce optimum yields of high purity oxygen vapor.

3. In a method of separating gaseou mixtures by low temperature fractionation in which separation takes place in a high pressure fractionation zone to provide a gaseous low boiling fraction and a low purity liquid high boiling fraction and in which the low purity liquid high boiling fraction is fed to a low pressure fractionation zone to provide a gaseous low boiling component and a liquid, substantially pure, high boiling component: the improvement comprising- (a) expanding said gaseous low boiling fraction to reduce it temperature;

(b) heat exchanging said expanded gaseous low boiling fraction with some of the liquid high boiling fraction; and

(c) maintaining the temperature of the expanded gaseous low boiling fraction higher than the temperature of the liquid high boiling fraction to accomplish added vaporization of the liquid high boiling fraction in the high pressure fractionation zone,

(d) said higher temperature of the expanded gaseous low boiling fraction being accomplished by heat exchange with discharging vapor products and blending with the balance of the gaseous low boiling fraction prior to expansion.

4. The method of separating air to produce vaporous nitrogen and vaporous oxygen which comprises passing said air under a superatmospheric pressure of at least five atmospheres through a heat exchange zone in heat exchange with cold waste gas to lower the temperature of the air to substantially its dew point, introducing said pressurized low temperature air into a high pressure fractionation zone in the presence of reflux to establish a nitrogen vapor overhead, a condensed liquid nitrogen and a crude oxygen liquid bottoms, cooling a first portion of said nitrogen vapor by heat exchange with the hereinafter formed waste gas, subsequently expanding said cooled first portion of said nitrogen vapor to supply refrigeration for said heat exchange zone, expanding said crude oxygen liquid bottoms into the low pressure fractionation zone, expanding a second liquid portion of said nitrogen into the low pressure fractionation zone to provide reflux and separate a high purity oxygen vapor from a waste gas, and heat exchanging a portion of the crude oxygen bottoms liquid with the effluent of the expansion of the first portion of the nitrogen, said expanded nitrogen effluent being at a temperature lower than the portion of crude oxygen bottoms liquid whereby the crude oxygen bottoms liquid is further cooled before expansion into the low pressure fractionation zone and returning said portion of cooled crude oxygen bottoms liquid to the low pressure fractionation zone whereby the yield of nitrogen vapor with reference to oxygen vapor is greatly augmented.

5- Th method of separating air as claimed in claim UNITED STATES PATENTS 2,048,076 7/1936 Linde 6239 X 2,537,046 1/ 1951 Garbo 62-14 2,715,323 8/1955 Johnson 6214 6 Schuftan 6238 X Dennis 6230 X Vesque 6238 X Matsch 6224 Grunberg et a1. 6213 X NORMAN YUDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner. 

1. THE METHOD OF SEPARATING AIR TO PRODUCE VAPOROUS NITROGEN AND VAPOROUS OXYGEN WHICH COMPRISES PASSING SAID AIR UNDER A SUPERATMOSPHERIC PRESSURE OF AT LEAST FIVE ATMOSPHERES THROUGH A HEAT EXCHANGE ZONE IN HEAT EXCHANE WITH COLD WAST GAS TO LOWER THE TEMPERATURE OF THE AIR TO SUBSTANTIALLY ITS DEW POINT, INTRODUCING SAID PRESSUREIZED LOW TEMPERATURE AIR INTO A HIGH PRESSURE FRACTIONATION ZONE IN THE PRESENCE OF REFLUX TO ESTABLISH A NITROGEN VAPOR OVERHEAD, A CONDENSED LIQID NITROGEN AND A CRUDE OXYGEN LIQUID BOTTOMS, EXPANDING A FIRST PORTION OF SAID NITROGEN VAPOR IN A TURBOEXPANDER WITH WORK NECESSARY TO SUPPLY REFRIGERATION FOR SAID HEAT EXCHANGE ZONE, EXPANDING SAID CRUDE OXYGEN LIQUID BOTTOMS INTO THE LOW PRESSURE FRACTIONATION ZONE, EXPANDING A SECOND LIQUID PORTION OF SAID NITROGEN INTO THE LOW PRESSURE FRACTIONATION ZONE TO PROVIDE REFLUX AND SEPARATE A HIGH PURITY OXYGEN VAPOR FROM A COLD WASTE GAS, WITHDRAWING A PORTION OF SAID CRUDE OXYGEN LIQUID BOTTOMS AND PASSING SAID PORTION OF CRUDE OXYGEN LIQUID BOTTOMS IN HEAT EXCHANGE WITH THE EFFLUENT OF THE EXPANSION OF THE FIRST PORTION OF THE NITROGEN VAPOR TO HEAT SAID PORTION OF LIQUID BOTTOMS, AND RETURNING SAID HEAT EXCHANGED PORTION OF LIQUID BOTTOMS BACK IN ADMIXTURE WITH A CRUDE OXYGEN LIQUID BOTTOMS IN SAID HIGH PRESSURE FRACTIONATION ZONE. 